Internal screw positive rod displacement metering pump

ABSTRACT

A metering apparatus includes at least one pair of closed cylindrical housings each housing a fluid exchange port. A metering screw penetrates each housing longitudinally and rotates, first in clockwise, the then in counter-clockwise senses during alternate cycles of the method of the invention. Hollow rods are engaged with the screws so that the screws penetrate the rods and move the rods along the screws longitudinally within the housings by screw rotation. With the rods translating in a first direction a fluid is drawn into the housings alternately through the port, while with the rods translating in the opposing direction, the fluid is expelled from the same port. Plural sets of the pairs of closed housings are used with dual channel fluid switches to move the fluid into one of each of the pairs of housing on a first half of an operating cycle, and to draw the fluid from the one of the pairs of housings on the second half of the cycle, with the pairs of housings exchanging roles cyclically.

INCORPORATION BY REFERENCE: Applicant(s) hereby incorporate herein byreference, any and all U.S. patents, U.S. patent applications, and otherdocuments and printed matter cited or referred to in this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to metering pump systems and moreparticularly to a new pump design having relatively short length andhigh speed switching for continuous fluid flow.

2. Description of Related Art

The following art defines the present state of this field: Nichols etal., U.S. Pat. No. 4,089,624 describes a pumping system for dispensingcontrolled and variable amounts of fluids in predetermined quantitiesincluding a pump piston, which moves axially in a pump chamber. Thepiston is reciprocated by a drive lead nut cooperating with anon-rotatable lead screw attached to the piston. The piston is sealed tothe pump chamber by a seal element whose distance from the lead nut isfixed regardless of the position of the piston, thus protecting theseal. The rotatably driven lead nut includes a hollow driven shaft,containing lubricant, so that the lead screw is lubricated as it travelsinto the shaft of the lead nut. The motor for the system is a pulseoperated reversible stepping motor enabling accurate output from thepump, for example, between 0.01 ml/min to 9.99 ml/min as controlled bythe stepping motor. One motor may drive two pumps for a continuouscontrolled pumping system. If desired a flush mechanism may be used torinse the piston of any pumped material which adheres to the surface.

Hutchins et al., U.S. Pat. No. 4,245,963 describes a pump for precise,smooth delivery of liquid, particularly in liquid chromatographysystems, featuring two liquid displacement elements mounted forreciprocating movement in chambers connected in series with two checkvalves, one displacement element serving to accumulate some of theliquid delivered by the first element and to deliver the accumulatedliquid while the first element is refilling.

Patterson et al., U.S. Pat. No. 4,352,636 describes a pump for producinga substantially smooth and continuous outflow of liquid at relativelyhigh pressure having two piston assemblies flow connected in series. Thefirst piston assembly includes a pressure piston having a long suctionstroke and a relatively short and abrupt expulsion stroke. A valve atthe inlet of the pressurization piston allows flow to enter (but notexit), and a valve at the outlet of the pressurization piston allowsflow to exit (but not enter). The second piston assembly includes adamper piston which functions as a mechanically driven damper to smooththe outflow from the pressure piston. This smoothing is accomplished bystoring of the liquid displaced by the expulsion stroke of the pressurepiston and then delivering the stored pressurized liquid to the pumpoutlet during the suction stroke of the pressure piston. The drive forthe pistons is constructed to produce an increased outflow ofpressurized liquid for a short interval at the beginning of theexpulsion stroke of the pressure piston to compensate forcompressibility of the liquid at high pressure. At low pressure, thestepper motor drive is slowed down in response to the sensing of theincrease of the outflow during this short interval to maintain theoutflow smooth and continuous during this part of the cycle ofoperation.

Strohmeier et al., U.S. Pat. No. 4,883,409 describes a pumping apparatusfor delivering liquid at a high pressure, in particular for use inliquid chromatography, comprising two pistons which reciprocate in pumpchambers, respectively. The output of the first pump chamber isconnected via a valve to the input of the second pump chamber. Thepistons are driven by linear drives, e.g., ball-screw spindles. Thestroke volume displaced by the piston is freely adjustable bycorresponding control of the angle by which the shaft of the drive motoris rotated during a stroke cycle. The control circuitry is operative toreduce the stroke volume when the flow rate, which can be selected byuser at the user interface is reduced, thus leading to reducedpulsations in the outflow of the pumping apparatus. The pumpingapparatus can also be used for generating solvent gradients when amixing valve connected to different solvent containers is coupled to theinput of the pumping apparatus.

Snodgrass et al., U.S. Pat. No. 5,516,429 describes a fluid dispensingsystem which has first diaphragm pump means, a filter connected toreceive the discharge of said first pump, and accumulator/seconddiaphragm pump means connected to receive the discharge of said filter.Hydraulic fluids pumped by cylinder/piston/stepper assembliesindependently actuate each of the diaphragm pumps, providing accurate,controllable and repeatable dispense of the subject fluid.

Muratsubaki et al., U.S. Pat. No. 6,068,448 describes a high pressurehydraulic pump apparatus constituting a two-stage pressurizing hydraulicbooster combining a pair of plunger pumps. The first and second pumpsare driven into a push-pull synchronous operation at the equal strokewith each other. The per-stroke displacement of the first pump isgreater than that of the second pump. The first pump draws byself-suction the liquid from a reservoir while the second pump is on thepressurizing and delivery stroke. When the first pump is on the deliverystroke, the liquid pressurized to a certain intermediate pressure by thefirst pump is sucked into the second pump. During the next reversestroke the second pump further pressurizes and discharges the liquidwhile the first pump effects the suction stroke. At the finalpressurization by the second pump, the driving stroke length of the pumpis controlled to a limited value, which provides a minimum delivery flowrequired for the interior of a load vessel to attain a target pressurein accordance with the compressibility of the liquid and the detectionof a load pressure.

Ganzel, U.S. Pat. No. 6,079,797 describes a ball screw pump assemblyincluding a pump body having an axial bore defining a travel chamber anda pressure chamber. An input port and an output port are formed in thepressure chamber. A ball screw is provided in the travel chamber. Apiston is connected to the ball screw and slidably extends into thepressure chamber as the ball screw is rotated. The piston divides thepressure chamber into an input chamber having a maximum volume and anoutput chamber having a maximum volume which is less than the maximum ofthe input chamber. The ball screw pump assembly can be used in avehicular braking system.

Eden et al., U.S. Pat. No. 6,510,780 describes a reversibly actuatablefluid hydraulic pump for use in a hydraulically driven elevator. Thepump comprises a cylinder and a piston linearly actuatable within thecylinder by a ball screw race disposed over a spindle and connected tothe piston. The shaft of the piston is hollow to receive the spindle asthe piston is drawn along by virtue of the motion of the race along thespindle, and seals are provided at the free end of the piston whichsealingly engage against the walls of the cylinder, and on the cylinderwhich sealingly engage with the shaft of the piston. A further featureof the invention is the provision of a compressible gas between the endof the cylinder and the end of the piston so that the expansion thereofreduces the work required to move the piston out of the cylinder,whereas when the system is relaxing, the compressible gas provides extraresistance and thus a smoother motion.

Britton Price Limited, WO 00/32932 describes a reversibly actuatablefluid hydraulic pump for use in a hydraulically driven elevator. Thepump comprises a cylinder and a piston linearly actuatable within thecylinder by means of a ball screw race disposed over a spindle andconnected to the piston. The shaft of the piston is hollow to receivethe spindle as the piston is drawn along by virtue of the motion of therace along said spindle, and seals are provided at the free end of thepiston which sealingly engage against the walls of the cylinder, and onthe cylinder which sealingly engage with the shaft of the piston. Afurther feature of the invention is the provision of a compressible gasbetween the end of the cylinder and the end of the piston so that theexpansion thereof reduces the work required to move the piston out ofthe cylinder, whereas when the system is relaxing, the compressible gasprovides extra resistance and thus a smoother motion.

ISCO, Inc., WO 02/068954 describes a plurality of pumps each having acorresponding one of a plurality of pistons and a corresponding one of aplurality of cylinders are driven by one motor to draw and pump solventsimultaneously into corresponding columns. To form a gradient, the pumpsare connected to two-way valves that are connected alternately to afirst solvent and a second solvent, whereby the time said valve is in afirst position controls the amount of solvent drawn from the firstreservoir into said pumps and the amount of time in said second positioncontrols the amount of said second solvent drawn from the secondreservoir into said pumps and the solvent is mixed in the pumpingsystems. The detectors are photodiodes mounted to light guides in theflow cells that generate signals related to light absorbance andcommunicate with a controller, whereby the controller receives signalsindicating solute between the light guides and causes collection ofsolute. An over-pressure system compensates for pressure over apredetermined level.

The prior art teaches a controlled pumping system, a liquid pump forchromatography systems, a dual piston pump, a liquid high pressure pump,a fluid dispensing pump, a pressure hydraulic pump having synchronouslydriven reciprocating pistons, a dual action ball screw pump, a ballscrew driven pump, and a liquid chromatographic method and system, butdoes not teach a metering pump that is highly compact by enabling itsdrive screw to penetrate its displacement rod. The present inventionfulfills this need and provides further related advantages as describedin the following summary.

SUMMARY OF THE INVENTION

The present invention teaches certain benefits in construction and usewhich give rise to the objectives described below.

A metering apparatus includes at least one pair of closed cylindricalhousings each housing a fluid exchange port. A metering screw penetrateseach housing longitudinally and rotates, first in clockwise, the then incounter-clockwise senses during alternate cycles of the method of theinvention. Hollow rods are engaged with the screws so that the screwspenetrate the rods and move the rods along the screws longitudinallywithin the housings by screw rotation. With the rods translating in afirst direction a fluid is drawn into the housings alternately throughthe port, while with the rods translating in the opposing direction, thefluid is expelled from the same port. Plural sets of the pairs of closedhousings are used with dual channel fluid switches to move the fluidinto one of each of the pairs of housing on a first half of an operatingcycle, and to draw the fluid from the one of the pairs of housings onthe second half of the cycle, with the pairs of housings exchangingroles cyclically. The prior art does not fairly show or teach a meteringpump rod that moves on a threaded screw wherein the screw penetrates thepiston to achieve compact size.

A primary objective of the present invention is to provide an apparatusand method of use of such apparatus that provides advantages not taughtby the prior art.

Another objective is to provide such an invention capable of meteringflow of a semi-fluid.

A further objective is to provide such an invention capable of meteringan essentially continuous flow of the semi-fluid.

A still further objective is to provide such an invention capable ofmetering continuous flow of plural components of a compound and joiningthe components in a mixing stream.

A still further objective is to provide such an invention in a highlycompact size and in a simple arrangement of components.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the present invention. In suchdrawings:

FIG. 1 is a schematic elevational front view of the preferred embodimentof the invention shown in section with push-pull interactive meteringaction;

FIG. 1A is a schematic of a switch portion of FIG. 1 showing analternate position of a rotating conduit member thereof; and

FIG. 2 is a front elevational perspective view thereof defining thestructure and method of continuous metering of plural components of amixture.

DETAILED DESCRIPTION OF THE INVENTION

The above described drawing figures illustrate the invention in at leastone of its preferred embodiments, which is further defined in detail inthe following description.

The present invention is a metering pumping apparatus and method ofmetering of fluids, and particularly for semi-fluids or highly viscousfluids such as epoxy, waxes, tars and pastes, referred to herein simplyas “fluid” or “fluids” (not shown). It can be appreciated that thefluids metered with the present invention may be any fluid whatsoeverand is not limited to those listed or referred to herein. The presentfluid metering apparatus comprises one or more, i.e., plural pairs, ofmetering units, each having a cylindrical housing 10 and all of whichare essentially identical in construction and function. It can beappreciated that a single pair of the metering units, as shown in FIG.1, are used for dispensing a single fluid, while plural pairs of theunits, as shown in FIG. 2, will be advantageously used for dispensingmixtures of two or more fluids. Each of the housings 10 provides asingle fluid exchange port 14 which enabled the fluid to move into andout of the housing 10 as will be further described below. Now, withrespect to each of the housings 10, a screw 20 is aligned longitudinallywith the housing 10, while a means for rotating 30 is engaged with thescrew 20 for rotating the screw 20 alternately in clockwise andcounter-clockwise senses. It will be appreciated that the rotating means30 shown in FIGS. 1 and 2 enables the two screws 20 to always rotate inopposing senses. In the figures, it will be appreciated that a gear orsprocket is shown, but that any means for rotation known in the art maybe employed and will be operated according to this specification. Forinstance, a direct drive using electric or hydraulic motors may beemployed and connected directly to screws 20. In any drive meansemployed in this invention, the screws 20 must turn in opposing sensesat all times.

In each unit, A rod 40 provides a fixedly fastened nut 42 at one end ofthe rod 40, and the nut 42 is thrededly engaged with the screw 20, thescrew 20 penetrating into a hollow space 44 within the rod 40. It willbe appreciated that nut 42 may be a plate with a threaded hole 43 foraccepting the screw 20. The rod 40 linearly translates along the screw20 in response to rotation of the screw 20 and this is clearly shown inFIG. 1 which shows the rods 40 at lower and upper extreme positions onscrews 20. The port 14 is positioned at a distal end 12 of the housing10, preferably below the rod 40 as shown in FIG. 1, wherein, translationof the rod 40 toward and away from the port 14 draws the fluid into andexpels the fluid out of the housing 10 respectively. This occurs becausethe rod 40 is sealed by sliding seal 16 in a manner well known in theart, i.e., by o-rings, chevrons seals, etc. A means for physicallysupporting 5 the screws 20 and rotating means 30, shown in the figuresprevents screws 20 from moving other than rotating, and such supportingmeans 5 may be any well known mounting structure.

The means for rotating 30 is enabled for rotating the screws 20 of eachof the pairs of the housings 10 in opposing directions at any oneinstant, such that the fluid is expelled from one of the housings 10 ofeach of the pairs of housings, while the other of the housings 10 ofeach of the pairs of housings draws the fluid in, the drawing andexpelling taking place in an alternating, push-pull cycle within each ofthe pairs of the housings 10. It will be appreciated that the purpose ofthe pair of metering devices that comprise the present invention,operate to provide a continuous flow of a single fluid and how thisoccurs will be described below.

A means for fluid conduction 60, 70 and 70′ is comprised of a series oftubes or similar fluid passages, as shown in FIG. 1, and includes adouble-throw fluid switch 60, a commercially available rotating switch.In this switch 60 a rotating portion provides dual passages P1 and P2which may be aligned with tubes 70 and 70′ in alternate arrangements.The rotating portion may be positioned as shown in FIG. 1 where passageP1 is aligned for conducting fluid from the port 14 on the left, todischarge tube 70′, and passage P2 is aligned for conducting fluid fromsupply container 80 to port 14 on the right. As shown by the arrows, theflows occur simultaneously. The alternate position of the rotatingportion of switch 60 is shown in FIG. 1A where, with a rotation of 90degrees in the clockwise direction of switch 60, passage P1 is alignedfor conducting fluid from supply container 80 to port 14 on the left,and passage P2 is aligned for conducting fluid from port 14 on the rightto discharge tube 70′, again, simultaneously. In summary then, switch 60is enabled for directing the fluid to one of the housings 10 andsimultaneously directing fluid from the other of the housings 10 whenthe switch 60 is in a first position of the fluid switch. The switch 60further simultaneously enables directing fluid to the other of thehousings and directing fluid from the one of the housings when placed inits second position. Switch 60 is able to move between its two operatingpositions in milliseconds by rotating 90 degrees CW and then 90 CCWalternately, or by simply rotating in 90 degree increments sequentiallyin one rotation sense whereby passages P1 and P2 exchange roles aftereach two 90 degree movements. Either mode of operation of switch 60 willachieve a similar result. The rods 40 are able to reverse theirdirections nearly as fast as the 90 degree rotation of switch 60 so thatthe fluid that is exiting switch 60 via conduit 70′, for all practicalpurposes, moves with continuous flow.

As shown in FIG. 2, the fluid conduction means 60, 70, 70′ and 70″enables mixing of the fluids from at least two of the plural pairs ofcylindrical housings 10 and dispensing the mixture from tube 70″. Oneimportant application of this process is the dispensing of two-partepoxy resins and other mixtures requiring a catalyst or hardener. Otherplural component mixes may be similarly dispensed and such may have morethan two components.

Clearly the rate of flow R1 of the fluids from the switch 60 on the leftin FIG. 2 may be different from the rate of flow R2 from the switch 60on the right. In this manner, the preparation of two or more componentmixtures with unequal component amounts may be precisely controlled andcontinuously dispensed. Adapting rate of flow from each pair of units isaddressed below.

As defined above, the fluid metering method of the present inventioncomprising the steps of providing the distal fluid exchange port 14 ineach of the at least one pair of cylindrical housings 10, aligning thescrews 20 longitudinally with the housings 10, engaging the means forrotating 30 with the screws 20, rotating the screws 20 alternately inclockwise and counter-clockwise senses, engaging the nuts 42 on one endof the rods 40 with the screws 20 so that they are able to penetratewithin the hollow spaces 44 within the rods 40, drawing and expellingthe fluid through the ports 14 by linear translating of the rods 40along the screws 20 in response to their rotation by the rotating means30, positioning the fluid conduction means 60, 70 and 70′ relative to atleast one of the plural pairs of housing 10, in a first state orposition, wherein the fluid is directed away from one of the housings 10and toward another of the housings 10 in one-half of a metering cycle ofthe method, and in a second state or position of the conduction means60, 70 and 70′ directing the fluid toward the one of the housings 10 andaway from the another of the housings 10 in a second-half of themetering cycle of the method. Clearly, the pitch of the teeth shown onthe planar gears of the rotating means 30 and the pitch of the threadsshown on the screws 20 defines the resolution of the present meteringmethod, i.e., the smallest theoretical volume of the fluid that may bedispensed from tube 70′. The rate of flow of the fluid from each of theswitches 60 is dependent upon the rotational rate of rotating means 30and the screw lead of screws 20, i.e., the ratio of linear advance ofrod 40 for each rotation. The total volume of the housing 10 defines themaximum output per half cycle that the system is capable of dispensing.The volume of supply container 80 defines the total output capacity ofthe system before reloading of the supply container 80 is required. Attube 70″ a mixture of plural fluid components is dispensed.

In an alternate embodiment of the present invention, when the rod 40 istoo small in diameter to accept a screw 20, the screw may be mounted toone side of the rod 40, with the nut 42 laterally extensive in engagingthe screw, so that the rod 40 moves in parallel to the screw 20 which,as defined above, rotates but does not translate. All translation isconfined to the rod 40, as above. This embodiment is described here butnot shown in the figures and not claimed. This alternative embodimentprovides the benefits of the primary embodiment defined in thisapplication above, in that the screw 20 and rod 40 are related in such amanner as to provide a more compact machine since the rod 40 overlapsthe screw 20 in its motion within housing 10. In the above earlierdescribed embodiment by driving the rod 40 up and over screw 20, and inthis later described embodiment by driving the rod 40 along side thescrew 20.

While the invention has been described with reference to at least onepreferred embodiment, it is to be clearly understood by those skilled inthe art that the invention is not limited thereto. Rather, the scope ofthe invention is to be interpreted only in conjunction with the appendedclaims and it is made clear, here, that the inventor(s) believe that theclaimed subject matter is the invention.

1. A fluid metering apparatus comprising: a pair of cylindricalhousings, each of the housings providing: a fluid exchange port; a screwaligned longitudinally with the housing; a means for rotating, engagedwith the screw for rotating the screw alternately in clockwise andcounter-clockwise senses; a rod having, at one end thereof, a nut,engaged proximally with the screw, the screw penetrating into a hollowspace within the rod, the rod linearly translating along the screw inresponse to rotation thereof, the port positioned at a distal end of therod wherein, translation of the rod toward and away from the port drawsthe fluid into and expels the fluid out of the housing respectively; themeans for rotating enabled for rotating the screws of the housings inopposing directions such that the fluid is expelled from one of thehousings while the other of the housing draws the fluid in, in analternating, push-pull arrangement; a fluid conduction means including adouble-throw fluid switch, the switch enabled for directing the fluid toone of the housings and directing fluid from the other of the housingsin a first position of the fluid switch, and enabled for directing thefluid to the other of the housings and directing fluid from the one ofthe housings in a second position of the fluid switch.
 2. A fluidmetering apparatus comprising: plural pairs of cylindrical housings,each of the housings providing: a fluid exchange port; a screw alignedlongitudinally with the housing; a means for rotating, the rotatingmeans engaged with the screw for rotating the screw alternately inclockwise and counter-clockwise senses; a rod having, at one endthereof, a nut engaged with the screw, the screw penetrating into ahollow space within the rod, the rod linearly translating along thescrew in response to rotation thereof, the port positioned at a distalend of the housing wherein, translation of the rod toward and away fromthe port draws the fluid into and expels the fluid out of the housingrespectively; the means for rotating enabled for rotating the screws ofeach of the pairs of the housings in opposing directions such that thefluid is expelled from one of the housings of each of the pairs ofhousings, while the other of the housings of each of the pairs ofhousings draws the fluid in, the drawing and expelling taking place inan alternating, push-pull cycle within each of the pairs of housings;and a means for fluid conduction including a double-throw fluid switch,the switch enabled for directing the fluid to one of the housings anddirecting fluid from the other of the housings in a first position ofthe fluid switch, and further enabled for directing the fluid to theother of the housings and directing fluid from the one of the housingsin a second position of the fluid switch.
 3. The fluid meteringapparatus of claim 2 wherein the fluid conduction means enables mixingof the fluids from at least two of the plural pairs of cylindricalhousings.
 4. The fluid metering apparatus of claim 2 wherein the fluidmetering rates of the plural pairs of cylindrical housings are notequal.
 5. A fluid metering method comprising the steps of: providing adistal fluid exchange port in each of at least one pair of cylindricalhousings, and in each of the at least one pair of housings: aligning ascrew longitudinally with the housing; engaging a means for rotatingwith the screw; rotating the screw alternately in clockwise andcounter-clockwise senses; engaging a nut on one end of a rod with thescrew so that the screw is able to penetrate within a hollow spacewithin the rod; drawing and expelling the fluid through the port withlinear translating of the rod along the screw in response to rotationthereof, positioning a fluid conduction means relative to at least oneof the plural pairs of housing, in a first state wherein the fluid isdirected away from one of the housings and toward another of thehousings in one-half of a metering cycle of the method; and in a secondstate wherein the fluid is directed toward the one of the housings andaway from the another of the housings in a second-half of the meteringcycle of the method.
 6. The fluid metering method of claim 5 furthercomprising the step of mixing the fluids from at least two of the pluralpairs of cylindrical housings.
 7. The fluid metering method of claim 5further comprising the step of adjusting different fluid metering ratesfor the plural pairs of cylindrical housings.